Github user viirya commented on a diff in the pull request: https://github.com/apache/spark/pull/15238#discussion_r80851313 --- Diff: sql/catalyst/src/test/scala/org/apache/spark/sql/catalyst/optimizer/SetOperationSuite.scala --- @@ -76,4 +77,32 @@ class SetOperationSuite extends PlanTest { testRelation3.select('g) :: Nil).analyze comparePlans(unionOptimized, unionCorrectAnswer) } + + test("no more unnecessary distincts in multiple unions") { + val query1 = OneRowRelation + .select(Literal(1).as('a)) + val query2 = OneRowRelation + .select(Literal(2).as('b)) + val query3 = OneRowRelation + .select(Literal(3).as('c)) + + val unionQuery1 = Distinct(Union(Distinct(Union(query1, query2)), query3)).analyze + val optimized1 = Optimize.execute(unionQuery1) + val distinctUnionCorrectAnswer1 = + Distinct(Union(query1 :: query2 :: query3 :: Nil)).analyze + comparePlans(distinctUnionCorrectAnswer1, optimized1) + + val unionQuery2 = Union(Distinct(Union(query1, query2)), query3).analyze + val optimized2 = Optimize.execute(unionQuery2) + val distinctUnionCorrectAnswer2 = --- End diff -- yes.
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